Laser beam projecting device

ABSTRACT

A laser beam projecting device, comprising a laser light source for emitting a laser beam, a wavelength selecting film for allowing the laser beam from the laser light source to pass, and a birefringent optical member arranged on an optical axis closer to an exit side than the wavelength selecting film, wherein the wavelength selecting film is tilted so that an incident angle of the laser beam is in a range of 45° to 80°.

BACKGROUND OF THE INVENTION

The present invention relates to a laser beam projecting devicecomprising structure for shutting off a return beam of a laser beamemitted from a laser light source.

It is known that output of a laser light source for emitting a laserbeam is decreased when there is a return beam, and a surveying systemutilizing the laser beam has an arrangement to shut off the return beam.

FIG. 7 shows general features of an optical system of a conventionaltype laser beam projecting device, which has an operation to shut offthe return beam.

In FIG. 7, reference numeral 1 denotes a semiconductor laser, andreference numeral 2 denotes a condenser lens. Reference numeral 3denotes an anamorphic prism, which comprises two wedge-like prisms 4 aand 4 b having different collection angles in two directions ofcross-section of luminous flux. After passing through the anamorphicprism 3, a laser beam 5 is projected on a projection optical axis 6. Onthe projection optical axis 6, there are arranged a polarizing plate 7for transmittig P-polarized light and a ¼λ plate (birefringent opticalcomponent) 8. Reference numeral 9 denotes an optical component forreflecting the laser beam 5. The optical component is a reflectingmirror, for instance.

The laser beam 5 emitted from the semiconductor laser 1 is, forinstance, a linearly P-polarized light, and cross-section of luminousflux of the laser beam 5 is in elliptical shape. After the laser beam 5is turned to parallel luminous flux by the condenser lens 2, thecross-section of the luminous flux of the laser beam 5 is expanded in ashort axis direction by the two wedge-like prisms 4 a and 4 b of theanamorphic prism 3, and the laser beam 5 is shaped so that thecross-section of the luminous flux has circular shape.

After passing through the anamorphic prism 3, the laser beam 5 with theluminous flux turned to circular shape passes through the polarizingplate 7. The laser beam 5 is then converted to a circularly polarizedlight by the ¼λ plate 8 and is projected.

Being reflected by the optical component 9, the circularly polarizedreflected laser beam 5′ is converted to a linearly polarized light asthe reflected laser beam 5′ passes through the ¼λ plate 8. Further, thelinearly polarized reflected laser beam 5′ thus converted has adirection of polarization different by 90° with respect to the projectedlaser beam 5, and the reflected laser beam 5′ becomes S-polarized light.The polarizing plate 7 is arranged so as to allow the P-polarized lightto pass. Accordingly, the S-polarized reflected laser beam 5′ is shutoff by the polarizing plate 7 and does not reach the semiconductor laser1.

In the conventional type laser beam projecting device as describedabove, the returning of the reflected laser beam 5′ is shut off by acombination of the polarizing plate 7 and the ¼λ plate 8 arranged on theprojection optical axis 6, and the polarizing plate 7 is required to bearranged on the projection optical axis 6. This results in complicatedstructure of the optical system. Also, as the polarizing plate 7 isprovided, reflection occurs on both surfaces of the polarizing plate 7,and this causes loss of the laser beam.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a laser beamprojecting device, by which it is possible to shut off a return beamwithout separately providing a polarizing plate, and to simplifystructure of the laser beam projecting device.

To attain the above object, the present invention provides a laser beamprojecting device, which comprises a laser light source for emitting alaser beam, a wavelength selecting film for allowing the laser beam fromthe laser light source to pass, and a birefringent optical memberarranged on an optical axis closer to an exit side than the wavelengthselecting film, wherein the wavelength selecting film is tilted so thatan incident angle of the laser beam is in a range of 45° to 80°. Also,the present invention provides the laser beam projecting device asdescribed above, wherein the laser beam projecting device has ananamorphic prism, and the wavelength selecting film is formed on onesurface of wedge-like prisms, which constitute the anamorphic prism.Further, the present invention provides the laser beam projecting deviceas describe above, wherein the wavelength selecting film is formed on anincident surface, which is tilted at a range of 45° to 80° with respectto the laser beam entering to the anamorphic prism. Also, the presentinvention provides the laser beam projecting device as described above,wherein the wavelength selecting film is tilted in such manner that theincident angle of the laser beam is in a range of 60° to 70°. Further,the present invention provides the laser beam projecting device asdescribed above, wherein the wavelength selecting film is determineddepending on a wavelength and an incident angle of the laser beam. Also,the present invention provides the laser beam projecting device asdescribed above, wherein the wavelength selecting film is a long-passfilter or a short-pass filter.

According to the present invention, there are provided a laser lightsource for emitting a laser beam, a wavelength selecting film forallowing the laser beam from the laser light source to pass, and abirefringent optical member arranged on an optical axis closer to anexit side than the wavelength selecting film, and the wavelengthselecting film is tilted so that an incident angle of the laser beam isin a range of 45° to 80°. As a result, the wavelength selecting film hasdifference in transmission characteristics between the P-polarizingcomponent and the S-polarizing component, and the wavelength selectingfilm fulfills a function as a polarizing plate. Thus, it is possible toshut off the return beam without providing a polarizing plateseparately, and this makes it possible to design an optical system withsimplified structure.

According to the present invention, the laser beam projecting device hasan anamorphic prism, and the wavelength selecting film is formed on onesurface of wedge-like prisms, which constitute the anamorphic prism.Thus, the return beam can be shut off without providing a polarizingplate separately, and this leads to the simplified structure of theoptical system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematical drawing to show an arrangement of an embodimentof the present invention;

FIG. 2 (A), FIG. 2 (B) and FIG. 2 (C) each represents a drawing toexplain relation of a wavelength selecting film formed on a transparentplate with an incident angle of a laser beam. FIG. 2 (A) shows a casewhere the incident angle is 0°, FIG. 2 (B) shows a case where theincident angle is 45°, and FIG. 2 (C) a case where the incident angle is60°.

FIG. 3 (A), FIG. 3 (B) and FIG. 3 (C) each represents a drawing toexplain relation of an incident angle of the laser beam with respect tothe wavelength selecting film with transmittance. FIG. 3 (A) shows acase where the incident angle is 0°, FIG. 3 (B) shows a case where theincident angle is 45°, and FIG. 3 (C) a case where the incident angle is60°.

FIG. 4 is a schematical drawing of a laser rotary irradiating systemaccording to the present invention;

FIG. 5 is a schematical drawing to show an essential portion of anoptical system of the laser rotary irradiating system;

FIG. 6 is a block diagram of an LD driving unit of the laser rotaryirradiating system; and

FIG. 7 is a schematical drawing to show an arrangement of a conventionaltype laser beam projecting device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Description will be given below on the best mode to carry out thepresent invention referring to the drawings.

First, referring to FIG. 1, description will be given on a basicarrangement of an optical system of a laser beam projecting device. InFIG. 1, the same component as shown in FIG. 7 is referred by the samesymbol.

A laser beam 5 from a semiconductor laser 1 is shaped by the anamorphicprism 3 and the laser beam 5 is projected. A ¼λ plate 8 is provided on aprojection optical axis 6 of the laser beam 5.

A wavelength selecting film 11 is formed on at least one surface ofwedge-like prisms 4 a and 4 b, which constitute the anamorphic prism 3,e.g. on a surface facing to the semiconductor laser 1 of the wedge-likeprism 4 a. By forming the wavelength selecting film 11 on the surfacewhich is tilted at an angle of 45° or more with respect to an incidentaxis of the laser beam, the wavelength selecting film 11 fulfills thefunction as a beam splitter.

Next, description will be given on characteristics of the wavelengthselecting film 11 referring to FIG. 2 (A), FIG. 2 (B), FIG. 2 (C), FIG.3 (A), FIG. 3 (B), and FIG. 3 (C).

FIG. 2 (A), FIG. 2 (B) and FIG. 2 (C) each represents a case where thewavelength selecting film 11 (long-pass filter or short-pass filter) isformed on a transparent plate 12, the laser beam 5 enters to thetransparent plate 12, and an incident angle is changed to 0°, 45° and60° respectively. FIG. 3 (A), FIG. 3 (B) and FIG. 3 (C) each representschanges of transmittance of a P-polarizing component and a S-polarizingcomponent in each case. In FIG. 3 (B) and FIG. 3 (C), a symbol Prepresents a transmittance curve of the P-polarizing component, and asymbol S represents a transmittance curve of the S-polarizing component.

When the laser beam 5 enters the transparent plate 12, i.e. thewavelength selecting film 11, at an incident angle of 0°, i.e. at aright angle as shown in FIG. 2 (A), the state of transmittance withrespect to a wavelength of the laser beam 5 is the same for both theP-polarizing component and the S-polarizing component. At an wavelengthof λA, the transmittance exceeds about 90%. In this case, the wavelengthselecting film 11 is a mere wavelength selecting film.

Next, when the laser beam 5 enters the wavelength selecting film 11 atan incident angle of 45° as shown in FIG. 2 (B), a transmissionwavelength of the laser beam 5 is shifted toward a short wavelength sidein both the P-polarizing component and the S-polarizing component asshown in FIG. 3 (B), and the transmittance exceeds about 90% at thewavelength of λB for the P-polarizing component and at the wavelength ofλB′ for the S-polarizing component. Further, an amount of shift ishigher in the P-polarizing component, and there is occurred an area 13(as shown by diagonal lines in FIG. 3 (B)) in which the P-polarizedcomponent passes through while the S-polarizing component is shut off.Therefore, the wavelength selecting film 11 fulfills the equivalentfunction to a polarizing plate with respect to the wavelength, which isincluded in the area 13.

Further, when the laser beam 5 enters the wavelength selecting film 11at an incident angle of 60° as shown in FIG. 2 (C), the transmissionwavelength of the laser beam 5 is shifted further toward the shortwavelength side for both the P-polarizing component and the S-polarizingcomponent as shown in FIG. 3 (C), and the transmittance exceeds about90% at the wavelength of λC for the P-polarizing component and at λC′for the S-polarizing component. The difference of the transition amountbetween the P-polarizing component and the S-polarizing componentincreases further. The area 13 (shown by diagonal lines in FIG. 3 (C)),in which the P-polarising component passes through while theS-polarizing component is shut off, becomes larger than the case wherethe incident angle is 45°. In the case where the incident angle is 60°,too, the wavelength selecting film 11 fulfills the equivalent functionto that of the polarizing plate with respect to the wavelength, which isincluded in the area 13.

Thus, as shown in FIG. 2 (C) and FIG. 3 (C), in case the wavelengthselecting film 11 is tilted at an angle of 60° with respect to theincident angle and the laser beam 5 with the wavelength included in thearea 13 is used, the wavelength selecting film 11 can be used as apolarizing plate which transmits the P-polarizing component but shutsoff the S-polarizing component.

By using the characteristics of the wavelength selecting film 11 asdescribed above, the wavelength selecting film 11 is formed on at leastone surface of the wedge-like prisms 4 a and 4 b, and the wavelengthselecting film 11 is tilted at an angle as required, e.g. at 60° withrespect to the laser beam 5.

The P-polarized laser beam 5 emitted from the semiconductor laser 1 hasa wavelength included in the area 13. The laser beam 5 is turned toparallel luminous flux by the condenser lens 2. The P-polarized laserbeam 5 passes through the wavelength selecting film 11, andcross-section of the luminous flux is shaped in circular shape by thewedge-like prisms 4 a and 4 b of the anamorphic prism 3. After passingtrough the anamorphic prism 3, the laser beam 5 is converted to acircularly polarized light by the ¼λ plate 8 and is projected to theoptical component 9. As the reflected laser beam 5′ reflected by theoptical component 9 passes through the ¼λ plate 8 again, the laser beam5 is converted to an S-polarized light. The S-polarized reflected laserbeam 5′ is shut off by the wavelength selecting film 11 and does notreach the semiconductor laser 1.

It is suffice that the tilt angle of the wavelength selecting film 11 isdetermined so that there is a difference in the transmittingcharacteristics of P-polarizing component and S-polarizing component,and so that the area 13 can be obtained. A tilt angle in the range of40° to 80°, or more preferably in the range of 60° to 70°, is selected,for instance. If variation in a wavelength of LD, variation in film,etc. is taken into account, a wavelength range to be used as apolarizing beam splitter should be wider, and it is preferable that theincident angle is 60° or more. However, increase of the incident anglemeans the tilting of the component. If the incident angle is made toolarge, larger space is required and is not preferable. Thus, theincident angle is preferably in the range of 60° to 70°.

According to the present invention, the return beam can be shut offwithout providing a polarizing plate separately.

Referring to FIG. 4 to FIG. 6, description will be given below on anexample of a surveying system comprising the laser beam projectingdevice according to the present invention. In FIG. 4 to FIG. 6, the samecomponent as shown in FIG. 1 is referred by the same symbol.

The surveying system is a laser rotary irradiating system for forming ahorizontal reference plane by irradiating a laser beam in a horizontaldirection by rotary irradiation. The laser rotary irradiating systemprimarily comprises a laser beam projecting device 15, a tilt correctingsystem 16, a projection optical system 17, a rotary irradiating unit 18,and a photodetection system 19.

For a laser beam 5 emitted from the semiconductor laser 1, tilting of anoptical axis is corrected at the tilt correcting system 16. Then, thelaser beam 5 is projected along a vertical optical axis by theprojection optical system 17. The rotary irradiating unit 18 deflectsthe laser beam 5 in a horizontal direction and projects the laser beam 5by rotary irradiation. The laser beam 5 thus irradiated forms ahorizontal reference plane. As the laser beam 5 crosses a reflectingobject 20, the laser beam 5 is reflected by the reflecting object 20. Areflected laser beam 5′ passes through the rotary irradiating unit 18and is received and detected by the photodetection system 19. At thephotodetection system 19, a position, a direction, etc. of thereflecting object 20 are detected.

Light emission from the semiconductor laser 1 is driven and controlledby an LD driving unit 21 as shown in FIG. 6. A part of the laser beam 5emitted from the semiconductor laser 1 is split, and is then detected bya photodetection element 22 such as a photodiode, etc. A result ofphotodetection is fed back to an output current control circuit 23.Based on a photodetection signal, the output current control circuit 23issues a control signal to control light intensity of the laser beam 5to a certain fixed level and sends the control signal to a semiconductorlaser driving circuit 24. Based on the control signal, the semiconductorlaser driving circuit 24 drives the semiconductor laser 1.

The tilt correcting system 16 has a free liquid surface 25. The laserbeam 5 emitted from the semiconductor laser 1 is reflected by the freeliquid surface 25. As a result, even when the laser rotary irradiatingsystem is installed with tilting, the projection optical axis of theprojection optical system 17 is corrected to a vertical direction andthe tilting can be corrected.

On the projection optical axis 6 from the tilt correcting system 16 tothe projection optical system 17, the anamorphic prism 3 is provided,and one of the surfaces of the wedge-like prisms 4 a and 4 bconstituting the anamorphic prism 3 is tilted at an angle as requiredwith respect to the projection optical axis 6. For instance, theincident surface of the wedge-like prism 4 a is tilted at an angle of60° with respect to the projection optical axis 6 as shown in FIG. 1,and the wavelength selecting film 11 is formed on the incident surfaceof the wedge-like prism 4 a.

The projection optical system 17 comprises a reflecting mirror 26 fordeflecting the laser beam 5 in a vertical direction after the laser beam5 has passed through the anamorphic prism 3, a beam expander 27 forexpanding a diameter of the luminous flux of the laser beam 5 on areflection light optical axis of the reflecting mirror 26, an aperturereflecting mirror 28, and the ¼λ plate 8 which is a component element ofthe laser beam projecting device 15.

The rotary irradiating unit 18 comprises a pentagonal prism 31, whichdeflects the laser beam 5 in a horizintal direction after the laser beam5 has passed through an aperture 29 of the aperture reflecting mirror 18and the ¼λ plate 8. The pentagonal prism 31 is arranged on a rotaryholder 32 with a hollow portion inside. When the rotary holder 32 isrotated by a rotating motor 33, the laser beam 5 projected from therotary holder 32 is projected by rotary irradiation.

Being reflected by the reflecting object 20, the reflected laser beam 5′enters through the rotary irradiating unit 18 and is deflected by theaperture reflecting mirror 28 toward the photodetection system 19.

The photodetection system 19 comprises a condenser lens 34, a polarizingplate 35, a pinhole plate 36, and a photodetection element 37, and thephotodetection system 19 can receive and detect the reflected laser beam5′ from the reflecting object 20. The polarizing plate 35 is arranged toallow the S-polarizing component to pass.

A photodetection signal from the photodetection element 37 is sent to acontrol unit 38. Based on the photodetection signal, the control unit 38controls rotation of the rotating motor 33 in such manner that, forinstance, reciprocal scanning is performed at an angle as requiredaround the reflecting object 20.

Next, description will be given on operation of the laser beam 5 and thereflected laser beam 5′ of the laser rotary irradiating system.

From the semiconductor laser 1, the P-polarized linear laser beam 5 isemitted and has a wavelength included in the area 13. After beingreflected by the free liquid surface 25, the laser beam 5 passes throughthe wavelength selecting film 11. The form of the laser beam is shapedby the anamorphic prism 3, and the laser beam 5 is deflected in avertical direction by the reflecting mirror 26, and the beam diameter isexpanded as required. After passing through the aperture 29, andfurther, through the ¼λ plate 8, the laser beam 5 is converted to acircularly polarized light. At the rotary irradiating unit 18, the laserbeam 5 is deflected in a horizontal direction and is projected by rotaryirradiation.

After being reflected by the reflecting object 20, the reflected laserbeam 5′ enters through the rotary irradiating unit 18. Then, thereflected laser beam 5′ passes through the ¼λ plate 8 again, and thereflected laser beam 5′ is converted to an S-polarized linearlypolarized light.

The reflected laser beam 5′ is reflected by the aperture 29 toward thephotodetection system 19 and is converged to a photodetection surface ofthe photodetection element 37 by the condenser lens 34. The polarizingplate 35 allows only the S-polarizing component to pass and shuts offthe other disturbance light. The pinhole plate 36 allows a luminous fluxof a limited portion on the optical axis to pass and shuts off the otherdisturbance light so that only the reflected laser beam 5′ from thereflecting object 20 is received by the photodetection element 37.

After passing through the ¼λ plate 8, a part of the reflected laser beam5′ passes through the aperture 29 and enters the laser beam projectingdevice 15 as a return beam. Because the wavelength selecting film 11 istilted so that the P-polarized light is allowed to pass, the reflectedlaser beam 5′, i.e. S-polarized light, is shut off by the wavelengthselecting film 11 and does not enter the semiconductor laser 1.Therefore, decrease of output of the semiconductor laser 1 is prevented,and the laser beam 5 in stable condition is emitted from thesemiconductor laser 1.

In addition to the reflected light from the reflecting object 20, areflected light from the surfaces of optical components such as thepentagonal prism 31, etc. is included in the reflected laser beam 5′ asshown in FIG. 5. These reflected light components are converted toS-polarized lights when the light components pass through the ¼λ plate 8in an outgoing course and in a return course, and these reflected lightcomponents are shut off by the wavelength selecting film 11.

The ¼λ plate may be provided separately on each of the laser beamprojecting device 15 and the photodetection system 19 respectively. Forinstance, ¼λ plates may be provided between the anamorphic prism 3 andthe reflecting mirror 26 and may be provided between the aperturereflecting mirror 28 and the condenser lens 34 respectively.

In the above, description has been given on a case where the presentinvention is provided on a laser rotary irradiating system, while thepresent invention may be provided on an electro-optical (light wave)distance measuring system, etc. The present invention can be introducedin the same manner to an optical system, for which it is necessary toeliminate influence of the return beam.

1. A laser beam projecting device, comprising a laser light source foremitting a laser beam, a wavelength selecting film for allowing thelaser beam from said laser light source to pass, and a birefringentoptical member arranged on an optical axis closer to an exit side thansaid wavelength selecting film, wherein said wavelength selecting filmis tilted so that an incident angle of the laser beam is in a range of45° to 80°.
 2. A laser beam projecting device according to claim 1,wherein said laser beam projecting device has an anamorphic prism, andsaid wavelength selecting film is formed on one surface of wedge-likeprisms, which constitute said anamorphic prism.
 3. A laser beamprojecting device according to claim 2, wherein said wavelengthselecting film is formed on an incident surface, which is tilted at arange of 45° to 80° with respect to the laser beam entering saidanamorphic prism.
 4. A laser beam projecting device according to claim 1or 3, wherein said wavelength selecting film is tilted in such mannerthat the incident angle of the laser beam is in a range of 60° to 70°.5. A laser beam projecting device according to claim 1 or 3, whereinsaid wavelength selecting film is determined depending on a wavelengthand an incident angle of the laser beam.
 6. A laser beam projectingdevice according to claim 1 or 2, wherein said wavelength selecting filmis a long-pass filter or a short-pass filter.